Wikipedia has a good breakdown of egg mass by size for various countries here (I used the US data for the graphic): http://en.wikipedia.org/wiki/Chicken_egg_sizes. I ended up focusing more on relative size as compared to a large egg (medium = .88 of a large egg) in the guide because most US recipes use large eggs as a standard, so relative sizing helps with substitutions.

Thanks for the link to the Cornucopia Institute’s report – that looks like a great resource!

The same way they test for quality in other manufactured items: statistical sampling. Since the Grade is an indicator of freshness and other environmental conditions, they can crack open a few and deduce that the rest are similar.

Shouldn’t the top row be listed Grade B, A, AA , in that order? Then it would be consistent with the price of the egg, as the other rows are.

With regards to your question, you’re right – that order would be consistent with price. When I made the graphic, I meant for the arrow under the farming methods to refer to just the farming methods, and not the sizes and grades. I now see how that can be a little confusing and I’ll see if I can make it more clear in V2. Thanks for pointing it out!